Linear Amplifiers
Published on 17 January 2014 by Bo OZ2M

Linear Amplifiers

The GEMINI linear amplifier is an all new solid state linear amplifier with 300 W output available in 6, 4 and 2 m versions. Designed to fill a market gap between the low power outputs of transverters and smaller rigs and the 1kW plus amplifiers that not all users want or can afford the Gemini range combines low drive requirements with instant on solid state performance. Furthermore GEMINI is a complete turnkey solution incorporating an integral 50 V linear power supply so no external PSU is required. First production will be a 4 m and 6 m version to be followed with 6 m (50 MHz) and 2 m (144 MHz) versions.

  • Solid state instant-on design
  • Integral 50 V linear power supply
  • Advanced cooling design ensures high duty cycle operation for MGM modes with low fan noise
  • In-built sequencer
  • Full protection against overdrive, high SWR and over-temperature
  • Ultra compact all aluminium chassis measuring just 270 w x 300 d x 120 h mm
  • Input drive levels from 3 W – 25 W can be specified
Linear Amp Challenger

MML 70/100 Linear Amplifier

Microwave Modules produced their MML70/100S linear amplifier for many years. It was specified for 10W in for 100W RF output but they never produced more than about 75W. Their suppression of second harmonic is also poor and some have been measured with second harmonic output at about -40db. It is recommended that a good quality low-pass or band-pass filter is used in conjunction with these units. Ex-PMR Pye type filters are ideal and are widely available at radio rallies.
A later model was manufactured in the mid-1990s, which was reputed to produce a full 100w output.

The amplifier also contains a receive pre-amplifier using a 3SK88 but is fairly noisy and will only be of use if your receiver is particularly 'deaf'.
These amplifiers were extremely popular for the 4m band and although they are no longer manufactured new they are widely available second-hand. Despite the early model's mediocre RF performance they are rugged and dependable in their aluminium extruded housing.

Vine Communications are advertising VHF amplifiers for 6m and 4m from TE Systems. One model offers 140W output for 10W input.

Spectrum Communications offer receive preamps (including a mast-head type) and linear power amplifiers up to 60W output.

BNOS of Essex once produced a wide range of power supplies and linear amplifiers for the radio amateur, and will now still make linear amplifiers to order. Their products are also often seen on the second-hand market: look out for the LPM 70/10/100. This produces a true 100W output for 10W input, includes a receive preamplifier as well as a LED power output bargraph and SWR protection. These units are worth hunting out if you are looking for a 100W amplifier for the 4m band.

A200 amplifier

An ex-PMR linear amplifier which is ideal for the 4m band was manufactured by Pye of Cambridge. The A200 linear amplifier was designed to boost the output of AM mobile transceivers to about 50W PEP output. The E0 model (marked on the serial number plate) is designed to operate from 68 - 88 MHz and will tune to the 4m band without any modification. They are designed to operate from 13.8V and include RF VOX and RF changeover relays. The only modification which may be desirable is to provide a facility to hard-switch the amplifier to prevent the relays chattering in SSB operation. These units can be recognised by their black cast housing with a cabled input connector and chassis-mounted output connector. Don't be deceived the three core 'brown, blue, green' power cable - these amplifiers are for 13.8V DC operation. Again these units have been widely seen on surplus stands at radio rallies at bargain prices, particularly for the E0 versions.
Dave G1OGY has placed a copy of the service manual here and FRARS has put together this modification file.

The Bremi BRL-200 10m valve linear may be converted for 70MHz operation. See this article by Ian M0BCG